Semiconductor Device and Method

ABSTRACT

A method includes forming a first opening in a dielectric layer over a substrate, lining sidewalls and a bottom of the first opening with a conductive barrier layer, and depositing a seed layer over the conductive barrier layer. The method further includes treating the seed layer with a plasma process, and filling the first opening with a conductive material after the treating the seed layer.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor devicefabrication, and, in particular embodiments, to formation of contacts(also referred to as contact plugs) in semiconductor devices.

BACKGROUND

The semiconductor industry has experienced rapid growth due tocontinuous improvements in the integration density of a variety ofelectronic components (e.g., transistors, diodes, resistors, capacitors,etc.). For the most part, this improvement in integration density hascome from repeated reductions in minimum feature size, which allows morecomponents to be integrated into a given area.

As transistor sizes decrease, the size of each feature decreases. Inadvance processing technologies, the high aspect ratio of contactopenings, which will be filled subsequently to form contact plugs, maypose a challenge for conventional gap filling methods used to fill thecontact openings. There is a need in the art for processing methods thatcould accommodate the small feature sizes in advanced processtechnologies.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a Fin Field-Effect Transistor (FinFET);

FIGS. 2-16 are cross-sectional views of a FinFET device at variousstages of fabrication, in an embodiment;

FIGS. 17-19 are cross-sectional views of a FinFET device at variousstages of fabrication, in an embodiment; and

FIG. 20 illustrates a flow chart of a method of fabricating asemiconductor device, in accordance with some embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments of the present disclosure are discussed in the context offorming a FinFET device, and in particular, in the context of formingcontact plugs of FinFET devices. However, one skilled in the art willreadily appreciate that the methods disclosed in the present disclosuremay be used in other devices or applications, e.g., planar devices.

FIG. 1 illustrates an example of a FinFET 30 in a perspective view. TheFinFET 30 includes a substrate 32 having a fin 36. The substrate 32 hasisolation regions 34 formed thereon, and the fin 36 protrudes above andbetween neighboring isolation regions 34. A gate dielectric 38 is alongsidewalls and over a top surface of the fin 36, and a gate electrode 40is over the gate dielectric 38. Source/drain regions 42 and 44 are inthe fin on opposite sides of the gate dielectric 38 and gate electrode40. FIG. 1 further illustrates reference cross-sections that are used inlater figures. Cross-section B-B extends along a longitudinal axis ofthe gate electrode 40 of the FinFET 30. Cross-section C-C is parallel tocross-section B-B and is across a source/drain region 42. Cross-sectionA-A is perpendicular to cross-section B-B and is along a longitudinalaxis of the fin 36 and in a direction of, for example, a current flowbetween the source/drain regions 42 and 44. Subsequent figures refer tothese reference cross-sections for clarity.

FIGS. 2-16 are cross-sectional views of a FinFET device 100 at variousstages of fabrication in accordance with an embodiment. The FinFETdevice 100 is similar to the FinFET 30 in FIG. 1, except for multiplefins. FIGS. 2-5 illustrate cross-section views of FinFET device 100along cross-section B-B, and FIGS. 6-16 illustrate cross-section viewsalong cross-section A-A.

FIG. 2 illustrates a cross-sectional view of a substrate 50. Thesubstrate 50 may be a semiconductor substrate, such as a bulksemiconductor, a semiconductor-on-insulator (SOI) substrate, or thelike, which may be doped (e.g., with a p-type or an n-type dopant) orundoped. The substrate 50 may be a wafer, such as a silicon wafer.Generally, an SOI substrate includes a layer of a semiconductor materialformed on an insulator layer. The insulator layer may be, for example, aburied oxide (BOX) layer, a silicon oxide layer, or the like. Theinsulator layer is provided on a substrate, typically a silicon or glasssubstrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the substrate 50 may include silicon; germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP; or combinations thereof.

The substrate 50 may include integrated circuit devices (not shown). Asone of ordinary skill in the art will recognize, a wide variety ofintegrated circuit devices such as transistors, diodes, capacitors,resistors, the like, or combinations thereof may be formed in and/or onthe substrate 50 to generate the structural and functional requirementsof the design for the FinFET. The integrated circuit devices may beformed using any suitable methods.

Referring to FIG. 3, the substrate 50 shown in FIG. 2 is patternedusing, for example, photolithography and etching techniques. Forexample, a mask layer, such as a pad oxide layer 52 and an overlying padnitride layer 56, is formed over the substrate 50. The pad oxide layer52 may be a thin film comprising silicon oxide formed, for example,using a thermal oxidation process. The pad oxide layer 52 may act as anadhesion layer between the substrate 50 and the overlying pad nitridelayer 56 and may act as an etch stop layer for etching the pad nitridelayer 56. In some embodiments, the pad nitride layer 56 is formed ofsilicon nitride, silicon oxynitride, silicon carbide, siliconcarbonitride, the like, or a combination thereof, and may be formedusing low-pressure chemical vapor deposition (LPCVD) or plasma enhancedchemical vapor deposition (PECVD), as examples.

The mask layer may be patterned using photolithography techniques.Generally, photolithography techniques utilize a photoresist material(not shown) that is deposited, irradiated (exposed), and developed toremove a portion of the photoresist material. The remaining photoresistmaterial protects the underlying material, such as the mask layer inthis example, from subsequent processing steps, such as etching. In thisexample, the photoresist material is used to pattern the pad oxide layer52 and pad nitride 56 to form a patterned mask 58, as illustrated inFIG. 3.

The patterned mask 58 is subsequently used to pattern exposed portionsof the substrate 50 to form trenches 61, thereby defining semiconductorstrips 60 between adjacent trenches 61 as illustrated in FIG. 3. In someembodiments, the semiconductor strips 60 are formed by etching trenchesin the substrate 50 using, for example, reactive ion etch (RIE), neutralbeam etch (NBE), the like, or a combination thereof. The etch may beanisotropic. In some embodiments, the trenches 61 may be strips (viewedfrom in the top) parallel to each other, and closely spaced with respectto each other. In some embodiments, the trenches 61 may be continuousand surround the semiconductor strips 60. After semiconductor strips 600are formed, the patterned mask layer 58 may be removed by etching or anysuitable method.

FIG. 4 illustrates the formation of an insulation material betweenneighboring semiconductor strips 600 to form isolation regions 62. Theinsulation material may be an oxide, such as silicon oxide, a nitride,the like, or a combination thereof, and may be formed by a high densityplasma chemical vapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g.,a CVD-based material deposition in a remote plasma system and postcuring to make it convert to another material, such as an oxide), thelike, or a combination thereof. Other insulation materials and/or otherformation processes may be used. In the illustrated embodiment, theinsulation material is silicon oxide formed by a FCVD process. An annealprocess may be performed once the insulation material is formed. Aplanarization process, such as a chemical mechanical polish (CMP), mayremove any excess insulation material (and, if present, the patternedmask layer 58) and form top surfaces of the isolation regions 62 and topsurfaces of the semiconductor strips 60 that are coplanar (not shown).

In some embodiments, the isolation regions 62 include a liner, e.g., aliner oxide (not shown), at the interface between the isolation region62 and the substrate 50/semiconductor strip 60. In some embodiments, theliner oxide is formed to reduce crystalline defects at the interfacebetween the substrate 500 and the isolation region 62. Similarly, theliner oxide may also be used to reduce crystalline defects at theinterface between the semiconductor strip 60 and the isolation region62. The liner oxide (e.g., silicon oxide) may be a thermal oxide formedthrough a thermal oxidation of a surface layer of substrate 50, althoughother suitable method may also be used to form the liner oxide.

Next, the isolation regions 62 are recessed to form shallow trenchisolation (STI) regions 62. The isolation regions 62 are recessed suchthat the upper portions of the semiconductor strips 60 protrude frombetween neighboring isolation regions 62 and form semiconductor fins 64(also referred to as fins 64). The top surfaces of the isolation regions62 may have a flat surface (as illustrated), a convex surface, a concavesurface (such as dishing), or a combination thereof. The top surfaces ofthe isolation regions 62 may be formed flat, convex, and/or concave byan appropriate etch. The isolation regions 62 may be recessed using anacceptable etching process, such as one that is selective to thematerial of the isolation regions 62. For example, a chemical oxideremoval using a CERTAS® etch or an Applied Materials SICONI tool ordilute hydrofluoric (dHF) acid may be used.

FIGS. 2 through 4 illustrate an embodiment of forming fins 64, but finsmay be formed in various different processes. In one example, adielectric layer can be formed over a top surface of a substrate;trenches can be etched through the dielectric layer; homoepitaxialstructures can be epitaxially grown in the trenches; and the dielectriclayer can be recessed such that the homoepitaxial structures protrudefrom the dielectric layer to form fins. In another example,heteroepitaxial structures can be used for the fins. For example, thesemiconductor strips can be recessed, and a material different from thesemiconductor strips may be epitaxially grown in their place.

In an even further example, a dielectric layer can be formed over a topsurface of a substrate; trenches can be etched through the dielectriclayer; heteroepitaxial structures can be epitaxially grown in thetrenches using a material different from the substrate; and thedielectric layer can be recessed such that the heteroepitaxialstructures protrude from the dielectric layer to form fins.

In some embodiments where homoepitaxial or heteroepitaxial structuresare epitaxially grown, the grown materials may be in situ doped duringgrowth, which may obviate prior and subsequent implantations although insitu and implantation doping may be used together. Still further, it maybe advantageous to epitaxially grow a material in an NMOS regiondifferent from the material in a PMOS region. In various embodiments,the fins may comprise silicon germanium (SixGe1-x, where x can bebetween approximately 0 and 1), silicon carbide, pure or substantiallypure germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. For example, the available materials forforming III-V compound semiconductor include, but are not limited to,InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, andthe like.

FIG. 5 illustrates the formation of dummy gate structure 75 over thesemiconductor fins 64. Dummy gate structure 75 includes gate dielectric66 and gate 68, in some embodiments. Dummy gate structure 75 may furtherinclude mask 70. To form the dummy gate structure 75, a dielectric layer66 is formed on the semiconductor fins 64 and the isolation regions 62.The dielectric layer 66 may be, for example, silicon oxide, siliconnitride, multilayers thereof, or the like, and may be deposited orthermally grown according to acceptable techniques. In some embodiments,the dielectric layer 66 may be a high-k dielectric material, and inthese embodiments, the dielectric layer 66 may have a k value greaterthan about 7.0, and may include a metal oxide or a silicate of Hf, Al,Zr, La, Mg, Ba, Ti, Pb, multilayers thereof, and combinations thereof.The formation methods of dielectric layer 66 may include molecular-beamdeposition (MBD), atomic layer deposition (ALD), plasma-enhanced CVD(PECVD), and the like.

A gate layer 68 is formed over the dielectric layer 66, and a mask layer70 is formed over the gate layer 68. The gate layer 68 may be depositedover the dielectric layer 66 and then planarized, such as by a CMP. Themask layer 70 may be deposited over the gate layer 68. The gate layer 68may be formed of, for example, polysilicon, although other materials mayalso be used. In some embodiments, the gate layer 68 may include ametal-containing material such as TiN, TaN, TaC, Co, Ru, Al,combinations thereof, or multi-layers thereof. The mask layer 70 may beformed of, for example, silicon nitride or the like.

After the layers (e.g., 66, 68 and 70) are formed, the mask layer 70 maybe patterned using acceptable photolithography and etching techniques toform mask 70. The pattern of the mask 70 then may be transferred to thegate layer 68 and the dielectric layer 66 by an acceptable etchingtechnique to form gate 68 and gate dielectric 66, respectively. The gate68 and the gate dielectric 66 cover respective channel regions of thesemiconductor fins 64. The gate 68 may also have a lengthwise directionsubstantially perpendicular to the lengthwise direction of respectivesemiconductor fins 64.

FIGS. 6-16 illustrate the cross-section views of further processing ofthe FinFET device 100 along cross-section A-A (along a longitudinal axisof the fin). As illustrated in FIG. 6, lightly doped drain (LDD) regions65 are formed in the fins 64. LDD regions 65 may be formed by a plasmadoping process. The plasma doping process may implant N-type or P-typeimpurities in the fins 64 to form the LDD regions 65. In someembodiments, the LDD regions 65 abut the channel region of the FinFETdevice 100. Portions of the LDD regions 65 may extend under gate 68 andinto the channel region of the FinFET device 100. FIG. 6 illustrates anon-limiting example of the LDD regions 65. Other configurations,shapes, and formation methods of the LDD regions 65 are also possibleand are fully intended to be included within the scope of the presentdisclosure. For example, LDD regions 65 may be formed after first gatespacers 72 are formed.

Still referring to FIG. 6, after the LDD regions 65 are formed, a gatespacer 87 is formed on the gate structure. The gate spacer 87 mayinclude a first gate spacer 72 and a second gate spacer 86. In theexample of FIG. 6, the first gate spacer 72 is formed on opposingsidewalls of the gate 68 and on opposing sidewalls of the gatedielectric 66. The first gate spacer 72 may also extend over the uppersurface of the semiconductor fin 64 and the upper surface of theisolation region 62 (see FIG. 5). The second gate spacer 86 is formed onthe first gate spacer 72, as illustrated in FIG. 6. The first gatespacer 72 may be formed of a nitride, such as silicon nitride, siliconoxynitride, silicon carbide, silicon carbonitride, the like, or acombination thereof, and may be formed using, e.g., a thermal oxidation,CVD, or other suitable deposition process. The second gate spacer 86 maybe formed of silicon nitride, SiCN, a combination thereof, or the likeusing a suitable deposition method.

In an exemplary embodiment, the gate spacer 87 is formed by firstconformally depositing a conformal first gate spacer layer 72 over theFinFET device 100, then conformally depositing a second gate spacerlayer 86 over the deposited first gate spacer layer 72. Next, ananisotropic etch process, such as a dry etch process, is performed toremove a first portion of the second gate spacer layer 86 disposed onupper surfaces of the FinFET device 100 (e.g., the upper surface ofsemiconductor fins 64) while keeping a second portion of the second gatespacer layer 86 disposed along sidewalls of the gate structure. Thesecond portion of the second gate spacer layer 86 remaining after theanisotropic etch process forms the second gate spacer 86. Theanisotropic etch process also removes a portion of the first gate spacerlayer 72 disposed outside of the sidewalls of the second gate spacer 86,and the remaining portion of the first gate spacer layer 72 forms thefirst gate spacer 72.

The shapes and formation methods of the first gate spacer 72 and thesecond gate spacer 86 as illustrated in FIG. 6 are merely non-limitingexamples, and other shapes and formation methods are possible. Forexample, the second gate spacers 86 may be formed after the epitaxialsource/drain regions 80 (see FIG. 7) are formed. In some embodiments,dummy gate spacers are formed on the first gate spacer 72 before theepitaxial process of the epitaxial source/drain regions 80 illustratedin FIG. 7 and the dummy gate spacers are removed and replaced with thesecond gate spacers 86 after the epitaxial source/drain regions 80 areformed.

Next, as illustrated in FIG. 7, source/drain regions 80 are formed. Thesource/drain regions 80 are formed by etching the fins 64 to formrecesses, and epitaxially growing a material in the recess, usingsuitable methods such as metal-organic CVD (MOCVD), molecular beamepitaxy (MBE), liquid phase epitaxy (LPE), vapor phase epitaxy (VPE),selective epitaxial growth (SEG), the like, or a combination thereof.After the epitaxial growth of the source/drain regions 80, mask 70 maybe removed by a suitable method, such as etching.

As illustrated in FIG. 7, the epitaxial source/drain regions 80 may havesurfaces raised from respective surfaces of the fins 64 (e.g. raisedabove the non-recessed portions of the fins 64) and may have facets. Thesource/drain regions 80 of the adjacent fins 64 may merge to form acontinuous epitaxial source/drain region 80. In some embodiments, thesource/drain regions 80 for adjacent fins 64 do not merge together andremain separate source/drain regions 80. In some exemplary embodimentsin which the resulting FinFET is an n-type FinFET, source/drain regions80 comprise silicon carbide (SiC), silicon phosphorous (SiP),phosphorous-doped silicon carbon (SiCP), or the like. In alternativeexemplary embodiments in which the resulting FinFET is a p-type FinFET,source/drain regions 80 comprise SiGe, and a p-type impurity such asboron or indium.

The epitaxial source/drain regions 80 may be implanted with dopants toform source/drain regions 80 followed by an anneal. The implantingprocess may include forming and patterning masks such as a photoresistto cover the regions of the FinFET that are to be protected from theimplanting process. The source/drain regions 80 may have an impurity(e.g., dopant) concentration in a range from about 1E19 cm−3 to about1E21 cm−3. In some embodiments, the epitaxial source/drain regions maybe in situ doped during growth.

Next, as illustrated in FIG. 8, a first interlayer dielectric (ILD) 90is formed over the structure illustrated in FIG. 7, and a gate-lastprocess (sometimes referred to as replacement gate process) isperformed. In a gate-last process, the gate 68 and the gate dielectric66 (see FIG. 7) are considered dummy structures and are removed andreplaced with an active gate and active gate dielectric.

In some embodiments, the first ILD 90 is formed of a dielectric materialsuch as phosphosilicate glass (PSG), borosilicate glass (BSG),boron-doped phosphosilicate Glass (BPSG), undoped silicate glass (USG),or the like, and may be deposited by any suitable method, such as CVD,PECVD, or FCVD. A planarization process, such as a CMP process, may beperformed to planarize the top surface of the first ILD 90 such that thetop surface of the first ILD 90 is level with the top surface of thegate 68 (see FIG. 7). Therefore, after the CMP process, the top surfaceof the gate 68 is exposed, in some embodiments.

In accordance with some embodiments, the gate 68 and the gate dielectric66 directly under the gate 68 are removed in an etching step(s), so thatrecesses (not shown) are formed in each of the fins 64. Each recessexposes a channel region of a respective fin 64. Each channel region isdisposed between neighboring pairs of epitaxial source/drain regions 80.During the dummy gate removal, the dummy gate dielectric layer 66 may beused as an etch stop layer when the dummy gate 68 is etched. The dummygate dielectric layer 66 may then be removed after the removal of thedummy gate 68.

Further, in FIG. 8, a gate dielectric layer 96, a barrier layer 94 and agate electrode 98 are formed for replacement gate 97. The gatedielectric layer 96 is deposited conformally in the recess, such as onthe top surfaces and the sidewalls of the fins 64 and on sidewalls ofthe gate spacers 72, and on a top surface of the first ILD 90 (notshown). In accordance with some embodiments, the gate dielectric layer96 comprises silicon oxide, silicon nitride, or multilayers thereof. Inother embodiments, the gate dielectric layer 96 includes a high-kdielectric material, and in these embodiments, the gate dielectriclayers 96 may have a k value greater than about 7.0, and may include ametal oxide or a silicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, andcombinations thereof. The formation methods of gate dielectric layer 96may include MBD, ALD, PECVD, and the like.

Next, the barrier layer 94 is formed conformally over the gatedielectric layer 96. The barrier layer 94 may comprise an electricallyconductive material such as titanium nitride, although other materials,such as tantalum nitride, titanium, tantalum, or the like, mayalternatively be utilized. The barrier layer 94 may be formed using aCVD process, such as plasma-enhanced CVD (PECVD). However, otheralternative processes, such as sputtering or metal organic chemicalvapor deposition (MOCVD), atomic layer deposition (ALD), mayalternatively be used.

Next, the gate electrode 98 is deposited over the barrier layer 94, andfills the remaining portions of the recess. The gate electrode 98 may bemade of a metal-containing material such as TiN, TaN, TaC, Co, Ru, Al,combinations thereof, or multi-layers thereof, and may be formed by,e.g., electroplating, electroless plating, or other suitable method.After the formation of the gate electrode 98, a planarization process,such as a CMP, may be performed to remove the excess portions of thegate dielectric layer 96, the barrier layer 94, and the material of thegate electrode 98, which excess portions are over the top surface offirst ILD 90. The resulting remaining portions of material of the gateelectrode 98, the barrier layer 94, and the gate dielectric layer 96thus form a replacement gate 97 of the resulting FinFET device 100.

Next, in FIG. 9, a second ILD 95 is deposited over the first ILD 90. Inan embodiment, the second ILD 95 is a flowable film formed by a flowableCVD method. In some embodiments, the second ILD 95 is formed of adielectric material such as PSG, BSG, BPSG, USG, or the like, and may bedeposited by any suitable method, such as CVD and PECVD. Contactopenings 91 and 93 for contacts 102 (see FIG. 15 or FIG. 19) are formedthrough the first ILD 90 and/or the second ILD 95. For example, thecontact opening 91 is formed through the second ILD 95 and exposes thereplacement gate 97, while the contact openings 93 are formed throughthe first ILD 90 and the second ILD 95, and exposes source/drain regions80.

Next, in FIG. 10, a barrier layer 104 is formed over the second ILD 95.In some embodiments, the barrier layer 104 is conformally formed overthe second ILD 95 and lines sidewalls and bottoms of the contactopenings 91/93. The barrier layer 104 may comprise an electricallyconductive material such as titanium (Ti), titanium nitride (TIN),tantalum (Ta), tantalum nitride (TaN), or the like, and may be formedusing a CVD process, such as plasma-enhanced CVD (PECVD). However, otheralternative processes, such as sputtering or metal organic chemicalvapor deposition (MOCVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), may also be used. The barrier layer 104 may bereferred to as a conductive (e.g., electrically conductive) barrierlayer in the present disclosure.

In some embodiments, the barrier layer 104 comprises more than one layerof materials. For example, the barrier layer 104 may include a firstlayer (not individually illustrated) and a second layer (notindividually illustrated). The first layer comprises a firstelectrically conductive layer, and the second layer comprises a secondelectrically conductive layer different from the first electricallyconductive layer. The first layer of the barrier layer 104 may contactthe upper surface of the second ILD 95 and sidewalls of the ILDs 90/95exposed by the contact openings 91/93, the first layer may also contactthe epitaxial source/drain regions 80 and the metal gate 97. The secondlayer of the barrier layer 104 may be conformally formed over the firstlayer of the barrier layer 104, with the first layer disposed betweenthe first ILDs 900 or the second ILD 95 and the second layer. The firstlayer of the barrier layer 104 may comprise a first metal capable ofreacting with semiconductor materials (e.g., silicon, germanium) to formsilicide or germanide regions, such as nickel, cobalt, titanium,tantalum, platinum, tungsten, other noble metals, other refractorymetals, rare earth metals or their alloys. The first layer of thebarrier layer 104 reacts with the epitaxial source/drain regions 80 in asubsequent thermal anneal process to form silicide or germanide regions,in some embodiments. The second layer of the barrier layer 104 maycomprise a suitable material (e.g., TaN, TiN) that prevents thediffusion of metal layer 110 (see FIG. 14). In an exemplary embodiment,the first layer of the barrier layer 104 comprises a metal (e.g., Ta,Ti), and the second layer of the barrier layer 104 comprises a metalnitride (e.g., TaN, TiN).

Referring to FIG. 11, a thermal anneal process 510, such as a rapidthermal anneal (RTA) process, is performed after the barrier layer 104is formed. The thermal anneal process 510 forms silicide regions 82 atthe interface between the epitaxial source/drain regions 80 (e.g.,epitaxial silicon regions) and the barrier layer 104, in someembodiments. In other embodiments, the thermal anneal process 510 formsgermanide regions 82 at the interface between the epitaxial source/drainregions 80 (e.g., epitaxial germanium regions) and the barrier layer104. In yet other embodiments, the thermal anneal process 510 formssilicon germanide regions (e.g., a region comprising silicide andgermanide) 82 at the interface between the epitaxial source/drainregions 80 (e.g., epitaxial regions comprising silicon and germanium)and the barrier layer 104. In the illustrated embodiment, no silicide,germanide, or silicon germanide is formed at the interface between theILDs 90/95 and the barrier layer 104. In embodiments where the barrierlayer 104 does not include a first layer comprising a metal (e.g., Ti orTa) capable of forming a silicide or germanide, the thermal annealprocess 510 may be omitted.

Next, as illustrated in FIG. 12, portions of the barrier layer 104 overthe upper surface 95U of the second ILD 95 and along upper sidewalls ofthe contact openings 91/93 are removed. The removal of the portions ofthe barrier layer 104 may use a wet etch process, although othersuitable removal method may also be used. In an embodiment, a mask layer(not shown), such as a photo resist, is formed at the bottom of thecontact openings 91/93 to partially fill the contact openings 91/93,such that portions of the barrier layer 104 disposed on lower sidewallsand bottoms of the contact openings 91/93 are covered by the mask layer.Next, a wet etch process is performed to remove portions of the barrierlayer 104 that are not covered by the mask layer. After the wet etchprocess, the mask layer may be removed by a suitable process such asashing.

In some embodiments, a first distance D₁ between the upper surface 95Uof the second ILD 95 and an upper surface of the remaining portions ofthe barrier layer 104 in the contact openings 93 is between about 20 nmto about 35 nm, although other dimensions for the first distance D₁ arealso possible and may be determined by, e.g., the process technology anddesign. In some embodiments, a second distance D₂ between the uppersurface 95U of the second ILD 95 and an upper surface of the remainingportions of the barrier layer 104 in the contact opening 91 is betweenabout 20 nm to about 35 nm, although other dimensions for the seconddistance D₂ are also possible and may be determined by, e.g., theprocess technology and design. The first distance D₁ and the seconddistance D₂ may be the same in some embodiments. In other embodiments,the first distance D₁ and the second distance D₂ may be different fromeach other.

Next, as illustrated in FIG. 13, a second barrier layer is conformallyformed over the second ILD 95 and the remaining portions of the barrierlayer 104. In some embodiments, the second barrier layer comprises asame material (e.g., TiN, TaN) as the barrier layer 104, therefore, thesecond barrier layer and the remaining portions of the barrier layer 104are illustrated as a barrier layer 105 in FIG. 13. Note that due to theremaining portions of the barrier layer 104 (see FIG. 12) at the lowerportions of the contact openings 91/93, the barrier layer 105 has afirst width T₁ for upper portions of the barrier layer 105 and a secondwith T₂ for lower portions of the barrier layer 105, wherein T₂ islarger than T₁. The upper portions of the barrier layer 105 may refer tothe portions of the barrier layer 105 over the second ILD 95, and/orportions of the barrier layer 105 that extend into the contact openings91/93 by a depth less than or equal to D₁ (in contact openings 93) or D₂(in contact openings 91). The lower portions of the barrier layer 105may refer to portions of the barrier layer 105 that extend into thecontact openings 91/93 by a depth larger than a depth of D₁ (in contactopenings 93) or D₂ (in contact openings 91).

As illustrated in FIG. 13, the barrier layer 105 has a step shape atwhere the upper portion of the barrier layer 105 adjoins the lowerportions of the barrier layer 105. A first width W₁ of the contactopenings 93, measured between opposing upper portions of the barrierlayer 105, is larger than a second width W2 of the contact opening 93measured between opposing lower portions of the barrier layer 105.Similarly, a third width W₃ of the contact openings 91, measured betweenopposing upper portions of the barrier layer 105, is larger than afourth width W₄ of the contact opening 93 measured between opposinglower portions of the barrier layer 105.

In advanced semiconductor process, the high aspect ratio of openings(e.g., contact opening 91/93) may pose a challenge for formation oflayers (e.g., a conformal seed layer) within the openings usingdeposition methods such as PVD, or CVD. The wider opening (e.g., W₁ andW₃) at the upper portions of the contact openings 91/93 makes it easierfor the deposited material to enter the contact openings 91/93 and toform deposited layers, such as an insertion layer 106 (see FIG. 14) anda seed layer 108 (see FIG. 15), while the thicker barrier layer 105 atthe lower portions of the contact openings 91/93 may achieve bettermetal (e.g., copper) diffusion control.

Next, as illustrated in FIG. 14, an electrically conductive insertionlayer 106 is conformally formed over the barrier layer 105. In someembodiments, the insertion layer 106 comprises a noble metal, which mayresist chemical reactions (e.g., oxidization). The insertion layer 106may comprise tungsten nitride (WN), titanium nitride (TiN), ruthenium(Ru), platinum (Pt), the like, and may be formed by any suitableformation method such as PVD, CVD, or ALD, as examples. In an exemplaryembodiment, the barrier layer 105 is formed of TiN, and the insertionlayer 106 is formed of WN. A thickness of the conductive insertion layer106 is between about 5 angstrom to about 15 angstrom, in someembodiments. In some embodiments, the insertion layer 106 helps toreduce the roughness of a subsequently formed seed layer 108 (e.g., aseed layer comprising Co), thus preventing or reducing voids (e.g.,empty spaces) in the conductive layer 110 (see FIGS. 16 and 19) of thecontact plugs 102 formed in subsequent processing, details of which willbe described hereinafter. Without being limited to a particular theory,it is believed that seed layers formed over an oxide layer tend to haverough seed particles, which may cause voids in the conductive layerformed over the seed layer. By having the insertion layer (e.g., a noblemetal), oxidization is reduced or avoided, thus reducing the seedparticle size and resulting in a smoother seed layer, which in turnreduces or prevents voids in the conductive layer formed on the seedlayer.

After the insertion layer 106 is formed, a seed layer 108 is formed overthe insertion layer 106, as illustrated in FIG. 15. The seed layer 108may be deposited by PVD, ALD or CVD, and may be formed of tungsten,copper, or copper alloys, although other suitable methods and materialsmay alternatively be used. In an exemplary embodiment, the seed layer108 comprises cobalt (Co) and is formed using an ALD process. In theillustrated embodiment, the ALD process for forming the cobalt seedlayer 108 is performed using precursors including H₂ and DicobaltHexacarbonyl Tert-Butylacetylene (CCTBA), where the molecular structureof the CCTBA is Co₂(CO)6(HCC(CH3)). The precursor CCTBA used in the ALDprocess is in a liquid state, in some embodiments. In accordance withsome embodiments, the ALD process for forming the cobalt seed layer 108is performed using a carrier gas of Ar, at a temperature between about150° C. and about 200° C., such as 175° C., and at a pressure betweenabout to torr to about 20 torr, such as 15 torr. A flow rate for H₂ isbetween about 2000 standard cubic center meter per minute (sccm) andabout 8000 sccm, such as 4000 sccm, and a flow rate of carrier gas Ar isbetween about 200 sccm and about 600 sccm, such as 400 sccm, in someembodiments.

Once the seed layer 108 has been formed, the conductive material 110 maybe formed onto the seed layer 108, as illustrated in FIG. 16. Theconductive material 110 may comprise tungsten, although other suitablematerials such as aluminum, copper, tungsten nitride, ruthenium, silver,gold, rhodium, molybdenum, nickel, cobalt, cadmium, zinc, alloys ofthese, combinations thereof, and the like, may alternatively beutilized. Any suitable deposition method, such as PVD, CVD, ALD, plating(e.g., electroplating), and reflow, may be used to form the conductivematerial 110. In an exemplary embodiment, the conductive material 110 iscobalt (Co), and the conductive material 110 is formed by electroplatingthe conductive material 110 onto the seed layer 108, filling andoverfilling the contact openings 91/93.

Once the contact openings 91/93 have been filled, excess barrier layer105, insertion layer 106, seed layer 108, and conductive material 110outside of the contact openings 91/93 may be removed through aplanarization process such as chemical mechanical polishing (CMP),although any suitable removal process may be used. Contact plugs 102 arethus formed in the contact openings 91/93.

In some embodiments, when the seed layer 108 is formed, e.g., using anALD or a CVD process, the seed layer 108 may have a high percentage ofcarbon (e.g., higher than about 20 atomic percent). The carbon in theseed layer 108 may come from the precursor (e.g., CCTBA) used in thedeposition process of the seed layer 108. Such a high percentage (e.g.,larger than 20 at. %) of carbon may cause the seed particles (e.g., Coparticles) to be rough (e.g., having a size or a diameter larger thanabout 2 nm to about to nm). The rough seed particles may result in anon-continuous seed layer 108. For example, the seed layer 108 may haveholes or discontinuities that expose an underlying layer (e.g., theinsertion layer 106) of the seed layer 108. In the discussionhereinafter, the holes and the discontinuities of the seed layer 108 maybe used interchangeably, and the seed layer 108 that has holes ordiscontinuities may be described as being discontinuous. When platingwithout the insertion layer 106, voids (e.g., empty spaces) may beformed in portions of the conductive material 110 adjacent (e.g., over)the holes/discontinuities in the seed layer 108, due to the difficultyof plating the conductive material 110 over the holes/discontinuities.Voids in the contact plugs 102 increase the electrical resistance of thecontact plugs and adversely affect the reliability of the electricalconnection of the semiconductor devices formed.

The present disclosure reduces or prevents the formation of voids in theconductive material 110 of the contact plugs 102 by forming theinsertion layer 106 between the barrier layer 104 and the seed layer108. During the plating process, the conductive material 110 may beplated over the seed layer 108 and portions of the insertion layer 106exposed by the holes/discontinuities in the seed layer 108, thus theconductive material 110 may be formed continuously (e.g., with no orreduced voids) over the surfaces of the seed layer 108, regardless ofwhether there are holes or discontinuities in the seed layer 108. Thecontact plugs 102 formed in the present disclosure have little or novoids, thus having low electrical resistance and providing reliableelectrical connections for the semiconductor device formed.

FIGS. 17-19 illustrate cross-sections views of a FinFET device 100 atvarious stages of fabrication in accordance with another embodiment. Theprocessing step illustrated in FIG. 17 follows that illustrated in FIG.13, therefore, FIGS. 2-13 and 17-19 illustrate the processing steps ofanother embodiment.

As illustrated in FIG. 17, after the barrier layer 105 is formed, a seedlayer 108 is formed over the barrier layer 105. The seed layer 108 maybe deposited by PVD, ALD or CVD, and may be formed of tungsten, copper,or copper alloys, although other suitable methods and materials mayalternatively be used. In an exemplary embodiment, the seed layer 108comprises cobalt (Co) and is formed using an ALD process. In someembodiments, the ALD process for forming the cobalt seed layer 108 isperformed using precursors including H₂ and CCTBA (e.g., CCTBA in liquidstate), using a carrier gas of Ar, at a temperature between about 15° C.and about 200° C., such as 175° C., and at a pressure between about 100torr to about 20 torr, such as 15 torr. A flow rate for H₂ is betweenabout 2000 sccm and about 8000 sccm, such as 4000 sccm, and a flow rateof carrier gas Ar is between about 200 sccm and about 600 sccm, such as400 sccm, in some embodiments.

Next, in FIG. 18, a process 610 is performed to treat the seed layer 108such that a percentage of carbon in the seed layer 108 is reduced. Forexample, a plasma process using one or more reactive species may beperformed, and the reactive species may react with the carbon in theseed layer 108 to form a product (e.g., a gaseous product) that can beeasily removed from the deposition chamber, thereby reducing thepercentage of carbon in the seed layer 108. After the process 610 (e.g.,a plasma process) is finished, the seed layer 108 turns into treatedseed layer 109. In some embodiments, a plasma process 610 is performedusing a plasma of H₂. The plasma used in the plasma process 610 isgenerated in the deposition chamber, in accordance with an embodiment. Aflow rate for H₂ may be between about 2000 sccm to about 8000 sccm, suchas 4000 sccm. The pressure for the plasma process 610 may be betweenabout 2 torr to about 100 torr, such as 5 torr, and an RF power for theplasma process may be between about 200 watt to about 600 watt, such as400 watt. In some embodiments, the H₂ plasma reacts with the carbon inthe seed layer 108 and generates a gaseous product (e.g., CO), which isevacuated from the deposition chamber. The chemical reaction equationfor the plasma processing 610 using H₂ is given below:

Co(CO)_(x)(HC≡CtBu)+H₂→Co+xCO+(HC═HC-tBu)H  (1)

When the seed layer 108 is formed, e.g., using an ALD or a CVD process,the seed layer 108 may have a high percentage of carbon (e.g., higherthan about 20 at. %). As discussed above, such a high percentage ofcarbon may cause voids in the contact plugs formed subsequently, due tothe rough seed particles (e.g., Co seed particles). The plasma process610 disclosed herein reduces the percentage of carbon of the seed layer.In some embodiments, after the plasma process 610, the percentage ofcarbon of the treated seed layer log is below about 20 at. %. Loweringthe carbon percentage reduces the roughness (e.g., size) of the seedparticles, which in turn reduces the discontinuities or holes in thetreated seed layer 109. As a result, voids in the contact plugs 102 arereduced or prevented.

Next, in FIG. 19, the conductive material 110 may be formed onto thetreated seed layer log. The conductive material 110 may comprisetungsten, although other suitable materials such as aluminum, copper,tungsten nitride, ruthenium, silver, gold, rhodium, molybdenum, nickel,cobalt, cadmium, zinc, alloys of these, combinations thereof, and thelike, may alternatively be utilized. Any suitable deposition method,such as PVD, CVD, ALD, electroplating, and reflow, may be used to formthe conductive material 110. In an exemplary embodiment, the conductivematerial 110 is cobalt (Co), and the conductive material 110 is formedby electroplating the conductive material 110 onto the treated seedlayer log, filling and overfilling the contact openings 91/93.

Once the contact openings 91/93 have been filled, excess barrier layer105, treated seed layer 109, and conductive material 110 outside of thecontact openings 91/93 may be removed through a planarization processsuch as chemical mechanical polishing (CMP), although any suitableremoval process may be used. Contact plugs 102 are thus formed in thecontact openings 91/93.

Variations and modifications of the presently disclosed embodiments arepossible. For example, the formation of the replacement gate 97 mayfollow similar processing steps as discussed above for forming contactplugs 102. As an example, referring to FIG. 8, after the gate dielectriclayer 96 is formed, a seed layer (e.g., a Co seed layer) may be formedusing, e.g., ALD deposition, and the deposited seed layer may be treatedusing a plasma process (e.g., plasma process 610) to reduce its carbonpercentage (thus reducing its seed particle roughness), before a platingprocess is used to form gate electrode 98 over the treated seed layer,similar to the processing illustrated in FIGS. 17-19. As anotherexample, still referring to FIG. 8, after the gate dielectric layer 96is formed, a barrier layer, an insertion layer, and a seed layer aresuccessively formed over the gate dielectric layer 96, before a platingprocess is used to form the gate electrode 98, similar to the processingillustrated in FIGS. 10-16. The optional thermal anneal process 510 mayor may not be performed, depending on, e.g., the design.

As yet another example, the embodiment illustrated in FIGS. 17-19 may becombined with the embodiment illustrated in FIGS. 2-16. In particular,after the seed layer 108 is formed over the insertion layer 106 (asillustrated FIG. 15) and before the formation of the conductive material110 (as illustrated FIG. 16), a plasma process similar to the plasmaprocess 610 of FIG. 18 may be performed to reduce the carbon percentageof the seed layer 108. After the plasma process is finished, theconductive material 110 may be formed over the plasma treated seedlayer. These and other variations or modifications to the embodimentmethods disclosed herein are possible, and are fully intended to beincluded within the scope of the present disclosure.

FIG. 20 illustrates a flow chart of a method of fabricating asemiconductor structure, in accordance with some embodiments. It shouldbe understood that the embodiment method shown in FIG. 20 is merely anexample of many possible embodiment methods. One of ordinary skill inthe art would recognize many variations, alternatives, andmodifications. For example, various steps as illustrated in FIG. 20 maybe added, removed, replaced, rearranged and repeated.

Referring to FIG. 20, at step 1010, a first opening is formed in adielectric layer over a substrate. At step 1020, sidewalls and a bottomof the first opening are lined with a conductive barrier layer. At step1030, a seed layer is deposited over the conductive barrier layer. Atstep 1040, the seed layer is treated with a plasma process. At step1050, the first opening is filled with a conductive material after thetreating the seed layer.

Embodiments may achieve advantages. In one embodiment, by treating thedeposited seed layer with a plasma process before plating, the carbonpercentage of the treated seed layer is reduced (e.g., to lower thanabout 20 at. %). The lower carbon percentage reduces the roughness ofthe seed particles, thus reducing the holes/discontinuities of thetreated seed layer, which in turn reduces or prevents the formation ofvoids in the contact plugs. In another embodiments, a conductiveinsertion layer is formed between the barrier layer and the seed layer.The conductive insertion layer may facilitate the plating of conductivematerial (e.g., conductive material 110) continuously over the seedlayer, regardless of whether there are holes/discontinuities in the seedlayer. As a result, contact plugs with little or no voids are formed bythe methods disclosed in the present disclosure. Contact plugs with noor little voids provide reliable electrical connection for the deviceformed and have low electrical resistance.

In some embodiments, a method includes forming a first opening in adielectric layer over a substrate, lining sidewalls and a bottom of thefirst opening with a conductive barrier layer, and depositing a seedlayer over the conductive barrier layer. The method further includestreating the seed layer with a plasma process, and filling the firstopening with a conductive material after the treating the seed layer.

In other embodiments, a method of forming a contact in a semiconductordevice includes depositing a conductive barrier layer over sidewalls anda bottom of an opening in a dielectric layer of the semiconductordevice, forming a conductive insertion layer over the conductive barrierlayer, forming a seed layer over the conductive insertion layer, theseed layer having holes, and plating a conductive material over the seedlayer to fill the opening.

In yet other embodiments, a method of forming a Fin Field-EffectTransistor (FinFET) includes forming a fin protruding above a substrate,forming a dielectric layer over the fin, forming a first opening in thedielectric layer, the first opening exposing a source/drain region ofthe fin, and forming a conductive barrier layer lining the firstopening. Forming the conductive barrier layer includes depositing afirst conductive layer over sidewalls and a bottom of the first opening,and depositing a second conductive layer over the first conductivelayer, the second conductive layer being different from the firstconductive layer. The method further includes performing a thermalanneal process after forming the conductive barrier layer, depositing aseed layer comprising carbon over the conductive barrier layer, treatingthe seed layer to reduce a percentage of carbon in the seed layer, andplating a conductive material over the seed layer to fill the firstopening.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure. While this disclosure has been described withreference to illustrative embodiments, this description is not intendedto be construed in a limiting sense. Various modifications andcombinations of the illustrative embodiments, as well as otherembodiments of the disclosure, will be apparent to persons skilled inthe art upon reference to the description. It is therefore intended thatthe appended claims encompass any such modifications or embodiments.

1. A method comprising: forming a first opening in a dielectric layerover a substrate; lining sidewalls and a bottom of the first openingwith a conductive barrier layer, wherein the conductive barrier layeralong upper sidewalls of the first opening has a first thickness, andthe conductive barrier layer along lower sidewalls and the bottom of thefirst opening has a second thickness, the first thickness being smallerthan the second thickness, wherein there is a step change from the firstthickness to the second thickness; depositing a seed layer over theconductive barrier layer, wherein the seed layer comprises cobalt;treating the seed layer with a plasma process, wherein the plasmaprocess reduces a percentage of carbon in the seed layer to below about20 at. %; and filling the first opening with a conductive material afterthe treating the seed layer. 2.-5. (canceled)
 6. The method of claim 1,wherein the treating the seed layer comprises performing the plasmaprocess using H₂.
 7. The method of claim 1, wherein the filling thefirst opening comprises performing a plating process to fill the firstopening.
 8. The method of claim 1, further comprising forming aconductive insertion layer between the conductive barrier layer and theseed layer.
 9. The method of claim 8, wherein the conductive barrierlayer comprises TiN, and the conductive insertion layer comprises WN.10. The method of claim 1, wherein after the depositing the seed layer,the seed layer has holes or discontinuities, wherein the treating theseed layer reduces the holes or the discontinuities of the seed layer.11. A method of forming a contact in a semiconductor device comprising:depositing a conductive barrier layer over sidewalls and a bottom of anopening in a dielectric layer of the semiconductor device, whereindepositing the conductive barrier layer comprises: conformallydepositing a first conductive barrier layer over the sidewalls and thebottom of the opening; removing first portions of the first conductivebarrier layer disposed over upper sidewalls of the opening while keepingsecond portions of the first conductive barrier layer disposed overlower sidewalls and the bottom of the opening; and conformallydepositing a second conductive barrier layer over the upper sidewalls ofthe openings and over the second portions of the first conductivebarrier layer, wherein after conformally depositing the secondconductive barrier layer, the conductive barrier layer has a step shapeat where an upper portion of the conductive barrier layer adjoins alower portion of the conductive barrier layer; forming a conductiveinsertion layer over the second conductive barrier layer; forming a seedlayer over the conductive insertion layer, the seed layer having holes;and plating a conductive material over the seed layer to fill theopening.
 12. The method of claim 1, wherein the plating comprisesplating the conductive material over portions of the conductiveinsertion layer exposed by the holes in the seed layer.
 13. The methodof claim 11, wherein the conductive insertion layer comprises WN, TiN,Ru or Pt.
 14. The method of claim 11, wherein depositing the firstconductive barrier layer comprises: forming a first layer comprising afirst metal over the sidewalls and the bottom of the opening, the firstmetal capable of forming a silicide or germanide; and forming a secondlayer comprising a metal nitride over the first layer.
 15. The method ofclaim 14, further comprising performing an anneal process after formingthe second layer and before removing the first portions of the firstconductive barrier layer, wherein the anneal process forms a silicide, agermanide or a silicon germanide.
 16. The method of claim 11, furthercomprising after forming the seed layer and before plating theconductive material, performing a plasma process to reduce a percentageof carbon of the seed layer.
 17. A method of forming a Fin Field-EffectTransistor (FinFET) comprising: forming a fin protruding above asubstrate; forming a dielectric layer over the fin; forming a firstopening in the dielectric layer, the first opening exposing asource/drain region of the fin; forming a first conductive barrier layerlining the first opening, forming the first conductive barrier layercomprising: depositing a first conductive layer over sidewalls and abottom of the first opening; and depositing a second conductive layerover the first conductive layer, the second conductive layer beingdifferent from the first conductive layer; performing a thermal annealprocess after forming the first conductive barrier layer; forming a masklayer at the bottom of the first opening, the mask layer covering lowerportions of the first conductive barrier layer proximate the bottom ofthe first opening, the mask layer exposing upper portions of the firstconductive barrier layer; performing an etching process to remove theexposed upper portions of the first conductive barrier layer while themask layer shields the lower portions of the first conductive barrierlayer from the etching process; removing the mask layer after theetching process; forming a second conductive barrier layer over thefirst conductive barrier layer and over upper sidewalls of the firstopening, wherein the first conductive barrier layer and the secondconductive barrier layer form a non-conformal conductive barrier layer,wherein the non-conformal conductive barrier layer has a step shapebetween an upper portion and a lower portion of the non-conformalconductive barrier layer; depositing a seed layer comprising carbon overthe second conductive barrier layer; treating the seed layer to reduce apercentage of carbon in the seed layer; and plating a conductivematerial over the seed layer to fill the first opening.
 18. The methodof claim 17, wherein before treating the seed layer, the seed layercomprises more than 20 at. % of carbon, wherein after treating the seedlayer, the seed layer comprises less than 20 at. % of carbon.
 19. Themethod of claim 17, further comprising forming a conductive insertionlayer after forming the second conductive barrier layer and beforedepositing the seed layer.
 20. The method of claim 19, wherein theconductive insertion layer comprises WN, TiN, Ru, or Pt.
 21. The methodof claim 1, wherein lining sidewalls and a bottom of the first openingwith a conductive barrier layer comprises: forming a first conductivebarrier layer over the sidewalls and the bottom of the first opening;removing the first conductive barrier layer disposed over uppersidewalls of the first opening while keeping the first conductivebarrier layer disposed over lower sidewalls of the first opening andover the bottom of the first opening; and after the removing, forming asecond conductive barrier layer over the first conductive barrier layerand over the upper sidewalls of the first opening.
 22. The method ofclaim 21, wherein the second conductive barrier layer is formed of asame material as the first conductive barrier layer.
 23. The method ofclaim 1, wherein the plasma process is performed with a flow rate for H₂between about 2000 standard cubic center meter per minute (sccm) andabout 8000 sccm, a pressure between about 2 torr and about to torr, anda radio frequency (RF) power for the plasma process between about 200watt and about 600 watt.
 24. The method of claim 1, wherein the plasmaprocess uses an H₂ plasma, wherein the H₂ plasma reacts with carbon inthe seed layer to generate a gaseous product CO.